The present invention generally relates to a tumbler type of cylinder lock where turning the lock without the proper key is impossible to effect, and more particularly, to a tumbler type cylinder lock where it is difficult to manufacture a duplicate lock by reading the heights of the tumblers.
Cylinder locks, which are widely used in, for example, motorcar doors and key switch portions or building doors or the like, have a pivotal rotor provided within a holder, and, a plurality of tumblers retained within the rotor. When a key is removed, the pivoting of the rotor becomes impossible to effect, because the tumblers are projected into a groove in the inner peripheral face of the holder. When the key is inserted, the pivoting of the rotor is enabled because the tumblers are engaged within the rotor.
FIGS. 9 through 12 show a conventional example of the construction of this type of cylinder lock. A rotor 2 is pivotally accommodated in a holder 1. A spring 4 and a tumbler 5, urged in a direction so as to be externally projected from an external peripheral face 2a of the rotor 2 by the spring 4, are slidably accommodated within a key groove 3 of the rotor 2. When a key 6 is removed, a lock portion 5b of the tumbler 5 is adapted to be projected into a groove 1b of the holder 1 from the external peripheral face 2a of the rotor 2, in a position where a contact portion 5a of the tumbler 5 is in contact with an inner peripheral face 1a of the holder 1. Although the projection amount at this time is regulated by the contact of the contact portion 5a of the tumbler 5 against the inner peripheral face 1a of the holder 1, the projection amount becomes the same in size as a plurality of tumblers 5 are the same in the outer shape thereof. As shown in FIG. 11 and FIG. 12, the key insertion hole 5c is not the same in position for each tumbler 5, but is provided at respective position-corresponding to the height on the corresponding key. When the key 6 has been inserted as far as the given position, the key insertion hole 5c is pushed by a mountain 6a of the key 6, and the tumbler 5 moves so that the tip end of the lock portion 5b is adapted to be retracted as far as the external peripheral face of the rotor 2.
FIG. 9 is a drawing showing the position of the tumbler 5 with the key 6 being drawn out, with the respective tumblers 5 arranged in alternating directions reversed to each other, within the rotor 2. When the key 6 has been drawn out, each tumbler 5 to be projected in the same direction moves to the same position, with the position of the key insertion hole 5c becoming a position corresponding to the key mountain 6a. When the key 6 has been inserted as shown in FIG. 10, all the tumblers 5 are pushed by the corresponding key mountains, are moved respectively as far as a position where the lock portion 5b is not projected, and are engaged into the rotor 2, thus allowing the rotor 2 to be pivoted.
As the position of the key insertion hole 5c when the key 6 has been drawn out corresponds to the height of the corresponding key mountain 6a in the conventional construction as described hereinabove, a duplicate lock may be made by the reading of the position of the key insertion hole 5c of each tumbler 5 with, for example, a magnifying endoscope, so that the safety of the key 6 is damaged. Also, as the movement amount of each tumbler 5 is the same, the rotor 2 may be picked by clockwise rotation of the rotor 2 from the condition of, for example, FIG. 11 so as to depress the tumblers 5 one by one against the urging force of the spring 4, riding the lock portion 5b on the end portion 1c on the side of the groove 1b of the inner peripheral face 1a of the holder 1. Thus, this point becomes also a factor of lowering the safety of the key 6.